PSI - Issue 18

Girolamo Costanza et al. / Procedia Structural Integrity 18 (2019) 223–230 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 2 shows a spring of 10 turns and 7.6 mm average diameter which if compressed has initial length of 28 mm while after heating reaches the length of 41 mm.

Fig. 2. SMA spring in two different configurations: on the left “compressed spring“, on the right spring with its “memorized length”.

3. Results and discussion The main parameters, which have been taken into account in this work are the overall length of the spring, the number of turns, the average diameter and the pitch. In the first step of the work the characterization of the spring has been performed in order to determine the value of the stiffness and the elastic constant of each spring. All the springs, both in martensitic and austenitic phase, have been characterized measuring the force by means of a load cell at each corresponding length. To characterize the spring in the austenitic condition, it has been activated by an electrical power supply linking the end of the spring with clamps. Fig. 3 shows the process in the austenitic phase. In Table 2 the experimental elastic constant “k” are reported.

Table 2. Different values of experimental elastic constant for different types of springs. Spring (experimental) k martensite (N/m) k austenite (N/m) 13 Turns, Diameter 6.6 mm 225.5 366.2 13 Turns, Diameter 7.6 mm 168.5 235.5 15 Turns, Diameter 7.6 mm 147.1 216.7

Fig. 3. Characterization of the spring during the compression test.